MySQL의 hash table 구조 및 hash table 관련 operation에 대한 분석

1. MySQL with FaCE
안미진
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2. Contents
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• Hash Table Format
• Creating a Hash Table
• Insertion in Hash Table
• Deletion in Hash Table

3. Hash Table Format
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Type of hash table, type
Adaptive hash index flag, adaptive
Number of cells in the hash table, n_cells
Pointer to cell array, array
Number of mutexes or rw_locks, n_sync_obj
Synchronization objects (mutex or rw_lock), sync_obj
Heaps, heaps
Heap, heap
Magic number, magic_n
void* node
mutexes
rw_locks
hash_table_t

4. Hash Table Format
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• type: type of hash table
 HASH_TABLE_SYNC_NONE
 HASH_TABLE_SYNC_MUTEX
 HASH_TABLE_SYNC_RW_LOCK
• adaptive: TRUE if this is the hash table of the adaptive hash
index
• n_cells: number of cells in the hash table
• array: pointer to cell array
 node: hash chain node, NULL if none

5. Hash Table Format
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• n_sync_obj: the number of mutexes or rw_locks, must be a
power of 2 or 0
• sync_obj: synchronization objects
① mutexes: NULL or an array of mutexes used to protect segments of
hash table
② rw_locks: NULL or an array of read/write locks
• heaps: if this is non-NULL, hash chain nodes for external
chaining can be allocated from these memory heaps
• heap
• magic_n: magic number (76561114)

6. Creating a Hash Table
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buf_pool_
init()
buf_pool_init
_instance()
ha_create()
ha_create
_func()
hash_create()
Initialized
hash table
hash table
buf_pool
->page_hash

7. buf_pool_init_instance()
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• buf/buf0buf.cc:1349

8. ha_create()
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• include/ha0ha.h:110

9. ha_create_func()
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• ha/ha0ha.cc:67

10. hash_create()
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Allocate memory for
hash table and hash entries
Initialize the elements
of hash table
• ha/hash0hash.cc:293

11. ha_create_func()
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Create a hash table
protected by
rw_locks or mutex
for buf_pool
• ha/ha0ha.cc:80

12. Insertion in Hash Table
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buf_page_
get_gen()
buf_read_
page()
buf_read_
page_low() buf_page_init
_for_read()
buf_page_init()
buf_block_init_low()
buf_page_init_low()
HASH_INSERT
fil_io()
HASH_SEARCH
buf_LRU_get_free_block()

13. Page Hash - Hash Table
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14. HASH_SEARCH
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• include/hash0hash.h:197

15. buf_page_init()
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• buf/buf0buf.cc:3510

16. HASH_INSERT
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DATA
(hash entry)
NULL
DATA
(hash entry)
NULL
struct3333
(hash entry)
hash
entry
hash
entry
There is no hash entry
If there are other hash
entries, find last hash entry
and insert DATA into the
next of the last hash entry
• include/hash0hash.h:122

17. Deletion in Hash Table
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buf_LRU_get
_free_block()
buf_LRU_scan_and
_free_block()
buf_LRU_free
_page()
buf_LRU_block_
remove_hashed()
HASH_DELETE
buf_LRU_get
_free_only()
buf_page_can_relocate()

18. HASH_DELETE
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1. Check whether the next
hash entry of DATA is valid
2. Change the pointer to point
the next hash entry
DATA
(hash entry)
hash
entry
hash
entry
DATA
(hash entry)
hash
entry
hash
entry
(void*)-1
: invalid address
• include/hash0hash.h:158